Clyde Estuary: short-term mooring

[peaceful warrior]

We're planning to visit some of the standing stones and other Celtic sites in the Western Isles and along the west coast of Ireland this August. We aim to deliver the boat to the Clyde Estuary early in July and need to leave her on a secure deep water mooring within an hour of Glasgow airport for 3 weeks. She's 45ft (13m) and draws 7'4" (2.3m). Anyone know of anywhere that wouldn't expect 500 pounds? Thanks